1. Field of the Invention
The present invention relates to a blood viscosity measurement device and, more specifically, to a blood viscosity measurement device which non-invasively measures the viscosity of human blood.
2. Description of the Related Art
Inspection of a health condition has been broadly carried out by use of blood, but not only a numeric value of a blood component but also a flow of blood, that is, rheology (fluidity) of blood are important for correct inspection.
Moreover, one of indexes indicating the rheology of blood is blood viscosity. In general, the viscosity is referred to as “fluidity or adhesion of blood”.
Heretofore, the viscosity of the blood sampled from human body has been measured with a measurement device, a viscometer or the like using a micro channel.
However, there are problems that qualification is required for performing a method involving the sampling of the blood and that it is difficult to check the flow of blood on a daily basis.
To solve the problems, in recent years, there has been proposed a device which measures a flow rate of blood non-invasively (i.e., without incising a living body or sticking a needle) in Japanese Patent Application Laid-Open No. 2003-204964 by the present applicant.
In this technology, the flow rate of the blood is non-invasively measured from a change amount of frequency of a reflected wave obtained by transmitting an ultrasonic wave to the blood. Since the blood flows in a certain direction, the ultrasonic wave reflected by the blood changes in frequency owing to Doppler effect. The flow rate of the blood can be obtained from the amount of this frequency change.
Moreover, in the technology of Japanese Patent Application Laid-Open No. 2003-204964, waves reflected in two different directions are received, and an angle (direction in which the blood flows) formed between a sensor and a blood vessel can be measured from the change amounts of the frequencies of these reflected waves. Furthermore, the flow rate is more correctly obtained in consideration of the measured angle. The viscosity can be estimated from the measured flow rate of the blood.
However, while carrying out investigations, it has been found that the flow rate of the blood depends on not only the viscosity of the blood but also a thickness of the blood vessel.
That is, the flow rate of even the blood having a low viscosity is reduced in a thin blood vessel, and the flow rate of even the blood having a high viscosity increases in a thick blood vessel.
Therefore, it has been newly found that not only the flow rate but also the thickness of the blood vessel need to be measured and considered in order to evaluate the viscosity of the blood more correctly.
An object of the present invention is to measure a flow rate of blood and a thickness of blood vessel in deciding a viscosity of blood.